Rotary disc cutters are devices for cutting workpieces, such as gears, very rapidly. The cutters are usually designed whereby a single revolution of the rotary disc cutter produces one tooth space on a gear blank. When the rotary cutter has made as many revolutions as the gear blank has tooth spaces, the gear is completed.
The basic form of a rotary disc cutter is shown, for example, in U.S. Pat. No. 2,315,147 to Wildhaber. The cutter comprises a relatively large diameter cutter with a plurality of blades located about the periphery thereof. A gap is present between the last and first blades in order to permit indexing of the gear blank when the gap is abreast of the blank.
In general, both roughing and finishing blades are present on a rotary cutter. U.S. Pat. No. 2,327,296 to Wildhaber shows roughing blades being of gradually increasing height, up to the desired depth of a tooth slot, to enable each successive blade to cut deeper into the gear blank as the cutter revolves. During rough cutting the rotary cutter and the gear blank are usually held in a fixed position, although for gears of increased width, it may be necessary for the rotary cutter to translate relative to the gear in order to remove sufficient stock along the tooth length. Roughing blades are somewhat narrower than finishing blades in order to leave a slight amount of stock on the tooth surfaces for removal by the finishing blades. Since both the rotary cutter and gear are usually held stationary during rough cutting, roughing blades produce a generally complimentary-shaped surface profile on the gear. For example, a concave circular arcuate profiled roughing blade would produce a convex circular arcuate profile on a tooth surface.
Following roughing, the finishing blades form the final surface of the tooth. The finishing blades are usually of uniform height and, during finish cutting, the rotary cutter and the gear blank are translated relative to one another along the length of the gear tooth thus enabling the finishing blades to produce a finished surface across the entire length of the tooth surface.
Many variations of rotary disc cutters are known in the art. For example, rotary disc cutters comprising only roughing blades are known. It follows then that an accompanying rotary cutter comprising finishing blades is necessary to produce a finished gear. The sides of a tooth slot may be finished by a single rotary cutter comprising two blade groups, as disclosed in U.S. Pat. No. 2,315,147, for sequentially finishing the sides of a tooth slot. After the first group finishes a first side surface, the gear is "set-over", that is, rotated a defined amount, and the second side surface is finished by the second group of blades on the rotary cutter. A gap between the two blade groups permits the set-over or position change of the gear.
The side surfaces on both the roughing and finishing blades are generally of circular arcuate profile although other profile shapes, such as involute, are also known. Both roughing and finishing blades comprise an end or tip and two side surfaces. Usually in roughing blades, the profiles of the side surfaces are all circular arcs based on the same center of curvature with only the length of the blades increasing in the direction of cutter rotation. Finishing blades may also have a curvature based on the same center. Such finishing blades may be utilized in the production of spur and helical gears as discussed in the previously mentioned U.S. Pat. No. 2,327,296 to Wildhaber.
However, it is also known to modify the profiles of successive blades of rotary cutters. For example, U.S. Pat. No. 2,315,147 discloses that, for bevel gears, successive finishing blades may vary in profile shape each according to the position at which it is to cut along the length of the tooth as relative translational movement between the cutter and gear takes place during the finishing operation. The successive finishing blades comprise a varying radii of curvature to provide variation in profile curvature from end to end of the gear tooth. The varying profile shape approach may also be applied to the roughing blades.
Profiles of finishing blades may have the same radius of curvature but the centers of curvature may be spaced either uniformly or nonuniformly along a line parallel to the tangent of the tooth profile according to U.S. Pat. No. 2,267,181 to Wildhaber. This approach enables a single rotary cutter to produce gears having different variations in profile curvature along the length of the teeth. Varying the feed rate of the rotary cutter relative to the gear controls the profile curvature. This concept may also be applied to the roughing blades thus requiring relative translational movement between the rotary cutter and gear during the roughing operation.
Roughing blades having slightly relieved circular arcuate side surfaces are known from U.S. Pat. No. 2,327,296. Each side comprises a singular circular arc profile and the purpose of the relieved side surface is to prevent side surfaces of the blades from contacting the tooth profiles formed by the preceding roughing blades thus avoiding rubbing of the blades on the tooth slot being cut. Only the juncture of the sides with the tip and the tip itself actually remove stock material from the gear.
In view of the speed at which rotary disc cutters remove stock material from gear blanks, wear, due to increased heat at the cutting surfaces, is a major concern. Metal chips packing between successive blades may also occur if the shape of the removed chip is not correct or if not enough fluid is present to wash the chips away from between the blades. Metal chips that collect between successive cutting blades may become hot due to the heat generated by the rapid cutting speed and the heat, in turn, may cause the chips to bond to one another and to the cutting blades.
It is an object of the present invention to reduce or eliminate the above-mentioned problems without sacrificing the speed of the cutting process.
It is another object of the present invention to provide a cutting blade that permits improved cooling of the cutting surface thereof and enhances the removal of metal chips from the vicinity of the blades.
A further object of the present invention is to reduce the costs involved with cutter production while extending the useful life of a rotary disc cutter due to less wear and chip packing during the cutting process.